Traditional transport services in a connection-oriented network offer limited protection capabilities for services riding over the network. These protection schemes generally use a pre-planned protection path to back up the working path, thus only providing back up protection for the first failure. As a result, protection from subsequent failures is generally not supported. For example, to guarantee fast protection switching performance (e.g., <100 ms), three commonly used protection schemes are ‘1+1 protection,’ ‘1:1 protection,’ and ‘1:N protection.’
A service with 1+1 protection provides a customer with a pair of dedicated ‘working’ and ‘protect’ paths. With 1+1 protection, when the working path fails, a switchover to the protect path will occur enabling the customer to still receive its service. In the transport network, the protect path is pre-allocated, reserved, dedicated bandwidth which is used to simultaneously carry the same traffic as the working path.
A service with 1:1 protection provides a customer with a ‘working’ path and a shared ‘protect’ path. The scheme allows the protection path to be used to carry other preemptable traffic when the working path is in a normal operating mode. When the working path fails, the scheme will preempt the existing traffic on the protection path, then switch traffic on the previous working path over to the protect path enabling the customer to still receive its service. With 1:1 protection, the protection path is pre-allocated, but its bandwidth can be shared with other preemptable traffic.
A service with 1:N protection provides a single ‘protection’ path (either shared or dedicated) to protect N customers' ‘working’ paths. When any one of the N working paths fails, the scheme will switch in the protection path to replace the failed working path. When all N working paths are in normal state, the protection path can carry other preemptable traffic, just as the 1:1 scheme does.
Three common limitations with current protection schemes and services are (1) When the protect path becomes the ‘active’ path (i.e., the new ‘working’ path), effectively, there is no continuation of the same protection provided to the customer should the new ‘active’ path fail and the original failed path has not been repaired, (2) When the protect path fails while the working path operates normally, the protection for the working path is lost, and (3) When both working and protect paths fail, the communication is totally disrupted.